The present invention relates to medical imaging equipment and in particular to an imaging spectrometer for detection of skin cancer.
The early detection of skin cancer largely relies on visual inspection of the skin and, in particular, on identification of skin patches with asymmetrical outlines, border irregularity, mottled colors, and diameters larger than a 6 mm (the skin cancer “ABC's”). While visual inspection is particularly well suited to cancer of the skin, the human eye's ability to distinguish among light frequencies is limited. The human eye is sensitive to three broad frequency bands whose relative intensities create the perception of many colors. Frequencies outside those bands are not perceptible, different frequencies within those bands may not be distinguishable, and single frequencies in areas of overlap of the bands can not be reliably distinguished from the effect of two different frequencies of light within each band.
The visually observable characteristics of skin cancer cells provide reason to believe that spectral information could provide improved cancer detection. U.S. Pat. No. 4,515,165, issued May 7, 1985, describes a medical imaging system in which cancerous tissue is illuminated with different frequencies of light to provide for multi-spectral imaging of tissue. U.S. Pat. No. 5,782,770 issued Jul. 21, 1998 describes an alternative approach in which polychromatic light illuminates the tissue and a scanning slit spectrograph is used to analyze the reflected light. The spectrograph provides “hyperspectral” imaging providing spectral readings at multiple frequencies with a spectral resolution of less than 10 nm of wavelength.
In both of these systems the imaging process is delayed by either the need to switch between colors or to scan a slit over an area of the imaged object. This delay creates the potential for misregistration of the image and spectrum and possible distortion of the image or spectrum if there is any movement during the acquisition process. To the extent that the switching of colors or slit scanning process require moving mechanical components, the ability to manufacture a rugged, portable and practical field device, may be adversely affected.